Editing Cirrus cloud (section)

== Optical phenomena ==
[[File:CircumhorizonArcIdaho.jpg|thumb|alt=A rainbow section in the sky|Circumhorizontal arc|left]]

Cirrus clouds can produce several optical effects like [[halo (optical phenomenon)|halos]] around the Sun and Moon. Halos are caused by interaction of the light with hexagonal ice crystals present in the clouds which, depending on their shape and orientation, can result in a wide variety of white and colored rings, arcs and spots in the sky, including [[sun dog]]s,<ref name="McGraw-1" /> the [[46° halo]],<ref name="Diedenhoven-475">{{harvnb|Diedenhoven|2014|p=475}}</ref> the [[22° halo]],<ref name="Diedenhoven-475" /> and [[circumhorizontal arc]]s.<ref name="natlgeo-rainbow">{{cite news|last=Gilman|first=Victoria|title=Photo in the News: Rare "Rainbow" Spotted Over Idaho|url=http://news.nationalgeographic.com/news/2006/06/060619-rainbow-fire.html|access-date=30 January 2011|newspaper=National Geographic News|date=19 June 2006|archive-url=https://web.archive.org/web/20070107030605/http://news.nationalgeographic.com/news/2006/06/060619-rainbow-fire.html|archive-date=7 January 2007}}</ref><ref name="ucsb">{{cite web|title=Fire Rainbows |url=http://www.geog.ucsb.edu/events/department-news/618/fire-rainbows/|work=News & Events|publisher=University of the City of Santa Barbara Department of Geology|access-date=31 January 2011|date=29 August 2009|archive-url=https://web.archive.org/web/20110512173057/http://www.geog.ucsb.edu/events/department-news/618/fire-rainbows/|archive-date=12 May 2011}}</ref> Circumhorizontal arcs are only visible when the Sun rises higher than 58° above the horizon, preventing observers at higher latitudes from ever being able to see them.<ref>{{cite web|url=https://cloudatlas.wmo.int/en/circumhorizontal-arc.html|publisher=World Meteorological Organization|access-date=15 March 2022|title=Circumhorizontal arc|website=International Cloud Atlas|archive-date=3 May 2022|archive-url=https://web.archive.org/web/20220503184132/https://cloudatlas.wmo.int/en/circumhorizontal-arc.html|url-status=live}}</ref>

More rarely, cirrus clouds are capable of producing [[glory (optical phenomenon)|glories]], more commonly associated with liquid water-based clouds such as [[stratus cloud|stratus]]. A glory is a set of concentric, faintly-colored glowing rings that appear around the shadow of the observer, and are best observed from a high viewpoint or from a plane.<ref name="glory-weather.gov">{{cite web|url=http://www.weather.gov.hk/education/edu06nature/ele_glory1106_e.htm|title=The Mysterious Glory|publisher=The Hong Kong Observatory|access-date=27 June 2011|archive-date=3 April 2012|archive-url=https://web.archive.org/web/20120403033423/http://www.weather.gov.hk/education/edu06nature/ele_glory1106_e.htm|url-status=live}}</ref> Cirrus clouds only form glories when the constituent ice crystals are [[wikt:aspherical|aspherical]]; researchers suggest that the ice crystals must be between 0.009&nbsp;millimeters and 0.015&nbsp;millimeters in length for a glory to appear.<ref name="glory-1433">{{harvnb|Sassen|Arnott|Barnett|Aulenbach|1998|p=1433}}</ref>